The present invention relates to Mobile IP network technology. More specifically, this invention relates to mechanisms for optimizing communications between a Mobile Node supporting Mobile IP and a Correspondent Node, where the Mobile Node is a member of a Virtual Private Network (VPN).
Mobile IP is a protocol which allows laptop computers or other mobile computer units (referred to as “Mobile Nodes” herein) to roam between various sub-networks at various locations—while maintaining internet and/or WAN connectivity. Without Mobile IP or a related protocol, a Mobile Node would be unable to stay connected while roaming through various sub-networks. This is because the IP address required for any node to communicate over the internet is location specific. Each IP address has a field that specifies the particular sub-network on which the node resides. If a user desires to take a computer which is normally attached to one node and roam with it so that it passes through different sub-networks, it cannot use its home base IP address. As a result, a business person traveling across the country cannot merely roam with his or her computer across geographically disparate network segments or wireless nodes while remaining connected over the internet. This is not an acceptable state-of-affairs in the age of portable computational devices.
To address this problem, the Mobile IP protocol has been developed and implemented. An implementation of Mobile IP is described in RFC 2002 of the Network Working Group, C. Perkins, Ed., October 1996. Mobile IP is also described in the text “Mobile IP Unplugged” by J. Solomon, Prentice Hall. Both of these references are incorporated herein by reference in their entireties and for all purposes.
The Mobile IP process in a Mobile IPv4 environment are illustrated in FIG. 1. As shown there, a Mobile IP environment 2 includes the internet (or a WAN) 4 over which a Mobile Node 6 can communicate remotely via mediation by a Home Agent 8 and may also include a Foreign Agent 10. In the absence of a Foreign Agent, the Mobile Node 6 can obtain a topologically correct IP address (i.e., collocated IP address) and register this IP address with the Home Agent. Typically, the Home Agent and Foreign Agent are routers or other network connection devices performing appropriate Mobile IP functions as implemented by software, hardware, and/or firmware. A particular Mobile Node (e.g., a laptop computer) plugged into its home network segment connects with the internet through its designated Home Agent. When the Mobile Node roams, it communicates via the internet through an available Foreign Agent. Presumably, there are many Foreign Agents available at geographically disparate locations to allow wide spread internet connection via the Mobile IP protocol. Note that it is also possible for the Mobile Node to register directly with its Home Agent.
As shown in FIG. 1, Mobile Node 6 normally resides on (or is “based at”) a network segment 12 which allows its network entities to communicate over the internet 4 through Home Agent 8 (an appropriately configured router denoted R2). Note that Home Agent 8 need not directly connect to the internet. For example, as shown in FIG. 1, it may be connected through another router (a router R1 in this case). Router R1 may, in turn, connect one or more other routers (e.g., a router R3) with the internet.
Now, suppose that Mobile Node 6 is removed from its home base network segment 12 and roams to a remote network segment 14. Network segment 14 may include various other nodes such as a PC 16. The nodes on network segment 14 communicate with the internet through a router which doubles as Foreign Agent 10. Mobile Node 6 may identify Foreign Agent 10 through various solicitations and advertisements which form part of the Mobile IP protocol. When Mobile Node 6 engages with network segment 14, Foreign Agent 10 relays a registration request to Home Agent 8 (as indicated by the dotted line “Registration”). The Home and Foreign Agents may then negotiate the conditions of the Mobile Node's attachment to Foreign Agent 10. For example, the attachment may be limited to a period of time, such as two hours. When the negotiation is successfully completed, Home Agent 8 updates an internal “mobility binding table” which specifies the care-of address (e.g., a collocated care-of address or the Foreign Agent's IP address) in association with the identity of Mobile Node 6. Further, the Foreign Agent 10 updates an internal “visitor table” which specifies the Mobile Node address, Home Agent address, etc. In effect, the Mobile Node's home base IP address (associated with segment 12) has been shifted to the Foreign Agent's IP address (associated with segment 14).
Now, suppose that Mobile Node 6 wishes to send a message to a Correspondent Node 18 from its new location. In Mobile IPv4, a message from the Mobile Node is then packetized and forwarded through Foreign Agent 10 over the internet 4 and to Correspondent Node 18 (as indicated by the dotted line “packet from MN”) according to a standard internet protocol. If Correspondent Node 18 wishes to send a message to Mobile Node—whether in reply to a message from the Mobile Node or for any other reason—it addresses that message to the IP address of Mobile Node 6 on sub-network 12. The packets of that message are then forwarded over the internet 4 and to router R1 and ultimately to Home Agent 8 as indicated by the dotted line (“packet to MN(1)”). From its mobility binding table, Home Agent 8 recognizes that Mobile Node 6 is no longer attached to network segment 12. It then encapsulates the packets from Correspondent Node 18 (which are addressed to Mobile Node 6 on network segment 12) according to a Mobile IP protocol and forwards these encapsulated packets to a “care of” address for Mobile Node 6 as shown by the dotted line (“packet to MN(2)”). The care-of address may be, for example, the IP address of Foreign Agent 10. Foreign Agent 10 then strips the encapsulation and forwards the message to Mobile Node 6 on sub-network 14. The packet forwarding mechanism implemented by the Home and Foreign Agents is often referred to as “tunneling.” In the absence of a Foreign Agent, packets are tunneled directly to the Mobile Node 6 collocated care-of address.
The Mobile IP protocol for Ipv6 has been described in RFC 3775, entitled “Mobility Support in Ipv6,” published in June 2004, by Johnson et al. RFC 3775 discloses a protocol which allows nodes to remain reachable while roaming in IPv6. RFC 3775 is incorporated herein by reference for all purposes. As disclosed in “Mobility Support in IPv6,” the Home Agent generally advertises its address, which is obtained by a Mobile Node. In Mobile Ipv6, there is no Foreign Agent. However, an access router 10 is present to provide connectivity to the network. The Mobile Node then sends a Binding Update message to the Home Agent. The Home Agent then sends a Binding Acknowledgement message to the Mobile Node. The Binding Update and Binding Acknowledgement messages are protected in IPSec transport mode. The Home Agent creates a binding cache entry and a tunnel is established between the Mobile Node's care-of address and the Home Agent. When a Correspondent Node sends a packet to the Mobile Node, it is forwarded to the Mobile Node by the Home Agent via the tunnel that has been established.
Mobile operators and service providers assign private IP addresses to their subscribers. More specifically, mobile operators worldwide typically use private Dynamic Host Configuration Protocol (DHCP) or PPP IP Control Protocol (IPCP) address assignment to their mobile users due to the lack of IP addresses. When the users are accessing the internet, the private IP address assigned to a user is translated to a public address at the edge of the private network before the packets are sent via the internet. This function is typically referred to as Network Address Translation (NAT).
In a virtual private network (VPN), addresses used within the network are typically private IP addresses. In order for nodes within the VPN to communicate with nodes outside the VPN, NAT is typically performed to convert private to public addresses and vice versa. This address conversion is performed by a NAT module or device as set forth in RFC 1631, entitled “The IP Network Address Translator (NAT),” published in May 1994 by Egevang et al, which is incorporated herein by reference for all purposes.
Internet draft entitled, “Mobile IPv4 Traversal Across IPsec-based VPN Gateways” by S. Varaala and Stinghorn, published on Sep. 28, 2004, and available at “http://www1.etf.org/proceedings_new/04nov/IDs/draft-ietf-mip4-vpn-problem-solution-00.txt,” discloses a layered solution for VPN traversal, and is incorporated herein by reference for all purposes. Specifically, this solution requires two layers of tunneling at mobility layers and an additional layer of tunneling at the VPN layer. The first Mobile IP tunnel exists between the Home Agent and the Mobile Node to provide mobility inside the enterprise. A second Mobile IP tunnel exists between the Home Agent and the Mobile Node when the Mobile Node moves outside the enterprise network. In addition, a VPN tunnel also exists between the Mobile Node and a VPN headend. The VPN headend is also sometimes referred to as a “VPN concentrator.” The VPN headend is a network device that manages information associated with a VPN session. The VPN tunnel associated with a Mobile Node terminates at the VPN headend. In order to create a VPN session, a VPN client attaches to the VPN headend.
Since the VPN tunnel and the second Mobile IP tunnel are required when the Mobile Node roams outside the VPN, two different tunnels are used simultaneously to transport data between the Mobile Node and the VPN headend. These two layers of encapsulation result in significant overhead, particularly on wireless links.
In view of the above, it would be beneficial if Mobile VPN communications could be optimized.